The present invention relates to a porous soft material sealing gasket, in particular, a cylinder head gasket for internal combustion engines, comprising an asbestos fiber plate, which may be metallically reinforced, impregnated with agents which wholly or partially fill the free pores of the soft material. Such impregnating agents are preferably plastic in the final state and/or are elastically cross-linked.
Cylinder head gaskets are used as static seals and are clamped or bolted between the cylinder head and motor block of an internal combustion engine to seal the rigid, generally flat faces of these engine parts. Cylinder head gaskets serve the purpose of providing a satisfactory surface seal quality by compensating for the unevenness and roughnesses of the surfaces to be sealed. For this reason, they are made of material which are plastically or elastically deformable under pressure, and are often made of a fibrous material, such as, in particular, of a soft asbestos fiber layer in the form of a plate or disc, which is possibly provided with reinforcing metallic inserts or metal sheets. The starting material for such cylinder head gaskets generally is an asbestos fiber mass mixed with binders, such as natural or synthetic rubber in small quantities, which is formed into a generally flat fiber web sheet or layer which can then be stamped and cut into the desired shape of the gasket.
Soft material cylinder head gaskets for internal-combustion engines usually comprise a laminate of a sheet metal plate onto which plates of asbestos fiber webs are rolled on both sides of the metal plate. This results in metallic reinforcement of the fiber web. For optimum seal strength, good adhesion between the layers is necessary, and this is accomplished by providing the sheet metal plate with rough cut teeth on both sides at regular intervals. During rolling, these teeth anchor the asbestos fiber plates by pressing themselves into the soft material in such a manner that normally, their tips penetrate to the surface of the gasket.
Cylinder head gaskets generally contain passages which have been cut out for the combustion chamber, the coolant and the lubricant. In the region of these passages, the sealing edges must be particularly tight against the hot gases of the combustion chamber which gases are under high pressure, against the lubricant and against the coolant which might contain anti-freeze. A simple gasket made of asbestos fiber, binder and possibly embedded reinforcing metal plates is not sufficient for this purpose because the cross-sectional density of the porous asbestos fiber material is unsatisfactory and the media to be sealed can pass through the seal. An additional improvement in the density of the asbestos material is required.
In the past, in order to provide a better surface seal, the edges of the passages have been provided with a metal bordering casing or flange, usually of copper or iron. In addition, the cross-sectional density and cross-sectional sealing capability of the asbestos fiber layer has been improved by utilizing impregnating or saturating agents and thereafter vulcanizing and hardening the impregnating agent. The impregnating or saturating agents that have been used include solutions, dispersions, emulsions or latexes of polymerized or polymerizable substances.
For an impregnation such as the one described in German Auslegeschrift No. 2,304,558 corresponding to British Pat. No. 1,447,143, and corresponding to U.S. application Ser. No. 918,820, now U.S. Pat. No. 4,201,804 which is preferably done by immersion, an additional advantage of the use of the metal plates with rough cut teeth is that the impregnating agent can penetrate deeply into the asbestos fibers through the openings produced by the penetration of the rough teeth. Particularly in an impregnation in which the pores are only partially filled, the impregnating agent is thus more uniformly distributed into all pores over the entire cross section.
For optimum results, an impregnation performed in this manner requires that the rough metal teeth be produced with great precision so that they have a uniform configuration, particularly with respect to their tips. Such precise manufacture is, however, difficult to attain in practice and costly due to irregular wear of the cutting tools. Thus, the impregnation will not be of the desired quality at those points where, due to a smaller angle of inclination, the rough metal teeth have not completely penetrated the asbestos fiber layer. The resulting cylinder head gaskets have deformation characteristics and sealing qualities which differ from place to place and which do not match the machine parts to be sealed.
Moreover, the proper impregnation of porous soft material sealing plates without embedded rough metal teeth could prove even more difficult. Depending on the viscosity of the impregnating (saturation) agent, the plate thickness and the immersion time, the impregnating agent will penetrate the soft material to different depths and, accordingly, the resultant coating has different depths. Such gaskets might not then have optimum deformation characteristics and crosssectional sealing properties.